Under normal conditions, cell growth occurs throughout the life of the organism. Usually this proceeds in the manner that is normal for the particular part of the body of that organism, but occasionally in specific instances such as healing of tissues, additional growth is needed until the tissue is repaired, at which time it should cease, and normal functioning be resumed. Occasionally, however, the normal growth-inhibiting factors cease to operate and cell growth continues unchecked.
There are several clinical areas in which mammalian cell growth poses a problem. Atherosclerosis, a major cause of death in the western world, is commonly treated by the operation of angioplasty. This produces the immediate effect of dilation of the blood vessel, but there is a continuing problem of restenosis, i.e. narrowing of the blood vessel, because of the proliferation of smooth muscle cell, and the deposition of extracellular matrix proteins such as collagen.
Similar problems resulting from undesired cell growth may be encountered after other surgical treatments, such as the installation of prostheses, implanted sensors, or implanted capsules that contain cells or release drugs.
There are, moreover, several medical conditions in which undesired growth of cells occurs, sometimes with results that are disfiguring, as in the case of the “Elephant Man”, who suffered a number of highly visible growths of tissue. Previously thought to be a case of neurofibromatosis, it is now thought to be a very rare condition, known as the Proteus syndrome.
Where restenosis is concerned, because of the scale of the problem arising from the number of angioplasties now carried out with an aging population, and with the tendency among western peoples to adopt an unsatisfactory diet, there have been intensive efforts to alleviate restenosis, see the review article “Restenosis—an open file” by Gottsauner-Wolf et al. in Clin. Cardiol. 19, 347-356 (1996). A wide variety of pharmaceuticals have been studied, and some success has been achieved with platelet inhibitors, glycoprotein IIIb/IIIa receptor antagonists, and the use of intracoronary metallic stents. There is still, however, a need for effective means of alleviating the problem of stenosis.